1. Field of the Invention
The invention relates to a plasma display panel and, more particularly to, such the plasma display panel that improves a light emitting utilization efficiency.
The present application claims priority of Japanese Patent Application No.2001-002171 filed on Jan. 10, 2001, which is hereby incorporated by reference.
2. Description of the Related Art
Presently a plasma display panel is being developed as a flat panel display which substitutes for a CRT (Cathode Ray Tube)
FIG. 3 is a cross-sectional view for showing a conventional AC (Alternating Current) plane direction-discharge type of plasma display panel.
The above-mentioned conventional plasma display panel, as shown in FIG. 3, includes a rear-side glass substrate 7 and a front-side glass substrate 12.
The rear-side glass substrate 7 is provided with a plurality of linear data electrodes 6 covered by a white dielectric 5. The front-side glass substrate 12 is provided with a plurality of linear transparent electrodes 10 made up of a nesa film and a plurality of linear trace electrodes 11 which are covered by a protection layer 8 and a transparent dielectric 9. The rear-side glass substrate 7 and the front-side glass substrate 12 are sealed with a sealing material. There is formed a plurality of discharge cells 14, 14, . . . separated each other by partitions 4, 4, . . . between the rear-side glass substrate 7 and the front-side glass substrate 12. The partitions 4 on the white dielectric 5 serve as walls of the discharge cell 14, so that the white dielectric 5 and the partition 4 are covered by a white reflection layer 2 as a buffer layer and a fluorescent layer 1. In each discharge cell 14, there are placed the trace electrode 11 and the data electrode 6 as opposed to each other in a vertical direction. The plurality of trace electrodes 11 and the plurality of data electrodes 6 are formed in a matrix form as a whole. The discharge cell 14 encapsulates therein a rare gas mixture containing Nexe2x80x94Xe, Hexe2x80x94Nexe2x80x94Xe, or a like.
The fluorescent layer 1 is formed by applying regions made of red, green, and blue light-emitting phosphor (fluorescent material) powder to each fluorescent film thickness of 10 xcexcm or so on the inner surface of a predetermined cell. In this plasma display panel, an AC voltage is applied to the transparent electrode 10 on the side of the front-side glass substrate 12 with respect to the interior of the discharge cell 14 to give rise to surface discharge in order to excite phosphors making up of the fluorescent layer 1 by a vacuum ultraviolet ray generated by Xe-gas discharge, thus emitting a visible light.
Conventionally, phosphors making up of the fluorescent layer 1 have been manufactured by baking by use of flux. A phosphor particle obtained by this manufacturing method is a poly-crystal having an average particle diameter of a few micrometers. To transform such the phosphor into paste to thereby form the fluorescent layer 1, this fluorescent layer 1 is considered to have a film thickness of 10 xcexcm or so. This is because a thinner film of the fluorescent layer 1 is considered to reduce the number of phosphor particles that can be excited. A thicker film, on the other hand, narrows discharge space and also deteriorates reflecting effect of the white reflection layer 2 owing to the phosphor particles. Actually, a current plasma display plane has a light emitting efficiency of 1.0 [lm/W] or so, which is problematically low as compared to that of a CRT. If increasing in light emitting efficiency of the phosphor can be achieved, the luminance and hence the picture quality can be improved. Also, such improvements can reduce power dissipation.
With a conventional method for manufacturing fluorescent materials, emitted light intensity tends to decrease as the particle diameter decreases. Because it is possibly required to lower the baking temperature to suppress the size of the phosphor particle diameter deteriorates the crystallinity, thus decreasing in the emitted light intensity of the phosphor.
In contrast, to enhance the crystallinity in order to increase the emitted light intensity of the phosphor, the baking temperature must be raised, thus resulting in a larger size of the phosphor particle diameter.
The conventional phosphors have been manufactured at a high baking temperature of 1000xc2x0 C. or higher. In baking at such a high temperature, to obtain a crystal having a good light emitting characteristic, the particle size must be a few micrometers or more in diameter. That is, a phosphor particle with a particle diameter of 1 xcexcm or less manufactured by the conventional method has poor crystallinity, thus deteriorating the light emitting characteristic.
In view of the above, it is an object of the present invention to provide a plasma display panel having an improved light emitting characteristic, by obtaining a fluorescent material with good crystallinity.
According to a first aspect of the present invention, there is provided a plasma display panel, wherein a phosphor constituting a fluorescent layer of the plasma display panel is made of mono-crystal particles, the mono-crystal particles each having a diameter of 10-200 nm.
In the foregoing first aspect, a preferable mode is one wherein a reflection layer for reflecting a light emitted from the phosphor is provided below the fluorescent layer.
Another preferable mode is one wherein the reflection layer is made of white pigment powder. Also, a preferable mode is one wherein between the fluorescent layer and the reflection layer is provided a color filter layer for selectively transmitting only a predetermined-wavelength visible light.
A further preferable mode is one wherein the color filter layer is made of an inorganic pigment.
A still further preferable mode is one wherein the fluorescent layer has a film thickness of 0.05-1.0 xcexcm.
An additional preferable mode is one wherein the reflection layer has a film thickness of 1-20 xcexcm.
Another preferable mode is one wherein the inorganic pigment used to form the color filter layer has an average particle diameter of 10-200 nm.
A further preferable mode is one wherein the color filter layer has a film thickness of 10-200 nm.
Also, according to a second aspect of the present invention, there is provided a plasma display panel in which a rear-side glass substrate provided with a data electrode covered by a white dielectric and a front-side glass substrate provided with a transparent electrode and a trace electrode covered by a protecting layer and a transparent dielectric are both sealed by a sealing material, in which a discharge cell separated by a partition is formed, in which on the white dielectric and the partition is formed a fluorescent layer made of a fluorescent material, wherein a fluorescent layer is formed in such a manner as to cover the protecting layer of the front-side glass substrate, the fluorescent material of the fluorescent layer being made of mono-crystal particles having a particle diameter of 10-200 nm.
In the foregoing second aspect, a preferable mode is one wherein the fluorescent layer has a film thickness of 0.05-0.5 xcexcm.
With the above configurations, it has the following effects.
A first effect is an improvement in the efficiency of taking out emitted light. A phosphor particle is excited by a vacuum ultraviolet ray emitted by Xe-gas discharge to then emit visible light in every direction. Fluorescent light reflected by a white reflection layer 22 is not degraded due to scattering by the phosphor particles.
A second effect is that the phosphor particle can be utilized efficiently because the fluorescent layer has a film thickness of a few hundreds of nano-meters, which is almost equivalent to the depth by which the vacuum ultraviolet ray will penetrate into the fluorescent layer. A conventional phosphor particle has a particle diameter of a few microns, so that the vacuum ultraviolet ray cannot penetrate deep into the phosphor, which means that only such phosphor particles that are present on the surface of the fluorescent layer can be utilized.
A third effect is that a mono-crystal phosphor particle employed mitigates a process deterioration, thus enabling the light emitting efficiency of each of the phosphor particles.
A fourth effect is that a buffer layer is provided to thereby prevent a phosphor made of ultra-minute particles from being absorbed. That is, since the existing partition 24 material or a white dielectric 25 contains a glass component, the fluorescent film is loosened by heat during the baking of the fluorescent layer, thus readily taking in the phosphor made of ultra-minute particle. Once taken in, the phosphor made of ultra-minute particles cannot obtain excitation energy from the vacuum ultraviolet ray, thus disabling light emission. To solve this problem, the buffer layer is provided to thereby prevent the phosphor made of ultra-minute particles from coming in direct contact with the materials of the partition 24 or the white dielectric 25, thus enabling avoiding take-in of the phosphor made of ultra-minute particles.
The fifth effect is that a white reflection layer 22 provided as the buffer layer causes a light emitted from the phosphor made of ultra-minute particles to be reflected totally, thus enabling efficiently taking out the light emitted from the phosphor toward the front-side glass substrate 32a. 
The sixth effect is that an external light can be split by a color filter layer into light components corresponding to various fluorescent colors, thus improving contrast ratio.